BOXE. 49 



in different bones of the skeleton, as shown by Dr. Owen Rees. Thus, the bones 

 of the head, and the long bones of the extremities, contain more earthy matter 

 than those of the trunk ; and those of the upper extremity somewhat more than 

 the corresponding bones of the lower extremity. The humerus contains more 

 earthy matter than the bones of the forearm ; and the femur more than the 

 tibia and fibula. The vertebras, ribs, and clavicle, contain nearly the same 

 proportion of earthy matter. The metacarpal and metatarsal bones contain 

 about the same proportion as those of the trunk. 



Much difference exists in the analyses given by chemists as to the proportion 

 between the two constituents of bone at different periods of life. According to 

 Schreger and others, there is a considerable increase in the earthy constituents 

 of the bones with advancing years. Dr. Rees states, that this is especially 

 marked in the long bones, and the bones of the head, which, in the foetus, do 

 not contain the excess of earthy matter found in those of the adult. But the 

 bones of the trunk in the foetus, according to this analyst, contain as much 

 earthy matter as those of the adult. On the other hand, the analyses of Stark 

 and Von Bibra show, that the proportions of animal and earthy matter are 

 almost precisely the same at different periods of life. According to the analyses 

 of Von Bibra, Valentin, and Dr. Rees, the compact substance contains more 

 earthy matter than the cancellous. The comparative analysis of the same bones 

 in both sexes shows no essential difference between them. 



There are facts of some practical interest, bearing upon the difference which 

 seems to exist in the amount of the two constituents of bone at different periods 

 of life. Thus, in the child, where the animal matter predominates, it is not 

 uncommon to find, after an injury to the bones, that they become bent, or only 

 partially broken, from the large amount of flexible animal matter which they 

 contain. Again, in aged people, where the bones contain a large proportion of 

 earthy matter, the animal matter at the same time being deficient in quantity 

 and quality, the bones are more brittle, their elasticity is destroyed; and, hencej 

 fracture takes place more readily. Some of the diseases, also, to which bones 

 are liable, mainly depend on the disproportion between the two constituents 

 of bone. Thus, in the disease called rickets, so common in the children of 

 scrofulous parents, the bones become bent and curved, either from the super- 

 incumbent weight of the body, or under the action of certain muscles. This 

 depends upon some defect of nutrition, by which bone becomes deprived of its 

 normal proportion of earthy matter, whilst the animal matter is of unhealthy 

 quality. In the vertebra of a rickety subject, Dr. Bostock found in 100 parts 

 79.75 animal and 20.25 earthy matter. 



Development of Bone. In the foetal skeleton some bones, such as the long 

 bones of the limbs, are cartilaginous, others, as the cranial bones, are mem- 

 branous. 1 Hence two kinds of ossification are described the intra-cartilaginous 

 and the intra-membranous ; and to these a third is sometimes added, the sub- 

 periosteal, which is a variety of the second. 



In the intra-cartilaginous ossification the first step is that the cartilage cells 

 increase rapidly in number, and arrange themselves in rows, with the long axis 

 of the cell transverse to that of the future bone. The cells are closely packed, 

 and in some places are even wedged together, an appearance which is supposed 

 to be due to their cleavage horizontally. The accompanying illustration, taken 

 from Rollett's article in Strieker's "Handbuch der Lehre von den Geweben." 

 p. 95, will save much of minute detail, and make the accompanying description 

 intelligible. 



The intra-cellular matrix of the cartilage a is still semi-transparent, though 



1 The bones which are developed entirely in membrane are the occipital, as far as it enters 

 into the formation of the vault of the skull, the parietal and frontal bones, the squamous portion 

 of the temporal with the tympanitic ring, the Wormiau bones, the nasal, lachrymal, malar, palate, 

 upper and lower maxillary, and vomer ; also, apparently, the internal pterygoid plate and the 

 sphenoidal turbinated bones. 



